We assemble a simple charger for Lithium-ion batteries, practically from trash.
I have accumulated a large number of batteries from laptop batteries, 18650 format. While thinking about how to charge them, I decided not to bother with Chinese modules, and by that time I had run out of them. I decided to put two schemes together. Current sensor and BMS board from a mobile phone battery. Tested in practice. Although the scheme is primitive, it works successfully, not a single battery was damaged.
Charger circuit
Materials and tools
- USB cord;
- crocodiles;
- BMS protection board;
- plastic egg from kinder;
- two LEDs of different colors;
- transistor kt361;
- 470 and 22 ohm resistors;
- two-watt resistor 2.2 ohm;
- one diode IN4148;
- tools.
Making a charger
We disassemble the USB cable and remove the connector. I got it from some iPad.
We solder the wires to the crocodiles.
We weigh down the deep part of the plastic kinder; I filled the M6 nut with hot glue.
We solder our simple circuit. Everything is done by surface mounting and soldered onto the BMS board. I used a double LED, but you can use two single-color ones. The transistor fell out of old Soviet radio equipment.
We thread the wires into the hole in the second, shallow half of the plastic kinder. Solder the circuit.
We stuff everything compactly into a plastic egg. We make a hole for the LED.
Connect to USB port PC or Chinese charger, they still have little current.
Lights up orange while charging. Those. both LEDs light up.
When the charge is complete, the green light is on, the one connected through the IN4148 diode.
You can check the circuit by disconnecting it from the battery; the green LED will light up, indicating the end of the charge.
The first stage of creation lithium ion battery is to determine the requirements for the voltage value and the required operating time. Then the characteristics of the load, environment, overall dimensions and weight are specified. Modern portable devices will have increased requirements for battery thickness, so choosing prismatic or even open-frame formats will be preferable. If thickness is not a determining factor, then choosing 18650 cylindrical elements as structural parts will provide lower cost and better performance(in terms of specific energy intensity, safety and durability). (See also BU-301a: Variety of electric battery shapes).
Most batteries used in medical equipment, power tools, electric bicycles and even electric cars use 18650 cells. It would seem that the use of this cylindrical cell is not particularly practical due to the large volume it occupies, but its strengths are such as advanced and mass production technology , as well as the low cost per watt hour, argue otherwise.
As mentioned above, the cylindrical shape of the element is not ideal, since it leads to the formation of empty space in multi-element systems. But if we consider the issue from the point of view of the need for cooling, then this disadvantage turns into an advantage. For example, elements of standard size 18650 are used in the Tesla S85 electric car, where their total number reaches 7,000 pieces. These 7,000 cells form a complex battery system that uses both series connections to increase voltage and parallel connections to increase current. If one element in a series connection fails, the power loss will be minimal, and in a parallel connection such an element will be turned off by the protection system. Accordingly, there is no dependence of the entire battery on single cells, which allows for more stable operation.
There is no consensus among electric vehicle manufacturers regarding the use of standard sizes, but there is a trend towards using larger formats as this reduces the total number of cells in the battery and therefore reduces the cost of the protection system. Savings can reach 20-25 percent. But on the other hand, the use of large elements leads to an increase in the total cost of kWh. According to 2015 data, it is the Tesla S85 with 18650-size cells that has a lower cost per watt-hour compared to electric vehicles using large prismatic batteries. Table 1 compares the kWh costs of different electric vehicles.
Table 1: Comparison of cost per watt hour various models electric vehicles. Mass production of 18650-size cells reduces the cost of the batteries that use them.
* In 2015-2016, the battery power of the Tesla S85 increased from 85 kWh to 90 kWh. The Nissan Leaf also saw an increase - from 25 kWh to 30 kWh.
The battery being developed must meet safety standards not only during standard operation, but also in the event of failure. All energy sources, and electric batteries are no exception, eventually exhaust their resources and become unusable. There are also cases of premature, unpredictable failure. For example, after some incidents, the on-board lithium-ion battery of the Boeing 787 airliner was placed in a special metal container with ventilation to the outside. In Tesla electric vehicles, the battery compartment is additionally protected by a steel plate to prevent penetrating damage.
Large battery systems for highly loaded systems are forced-cooled. It can be implemented in the form of heat removal by a radiator, or it may include a fan to supply cold air. There are also liquid-cooled systems, but they are quite expensive and are usually used in electric vehicles.
1. Security aspects
Reputable electrical cell manufacturers do not supply lithium-ion cells to uncertified battery manufacturing companies. This precaution is quite justified, since the protection circuit in the battery being designed may be incorrectly configured in order to overestimate the performance, and the cells will be charged and discharged not in a safe voltage range.
The cost of a certified battery system for air transport or other commercial use can range from $10,000 to $20,000. Such a high price is concerning, especially knowing that manufacturers periodically change the electrical components used in such systems. A battery system with such new cells, although listed as a direct replacement for an older one, will again require new certifications.
The question is often asked: “Why is a battery certified if the elements that make it up are already approved?” The answer is quite simple - the end device, the battery, must also be tested to ensure it meets safety standards and is assembled correctly. For example, a malfunction of the same protection circuit can lead to a fire or even an explosion, and its testing is only possible in a finished battery.
Creation of a lithium-ion battery
Learn about the power supply design requirements for a lithium-ion electrochemical system.
Why collect it yourself? Yes, because batteries are an area where the finished product is always crap. They are always unreasonably expensive. You can never get the right size, which is, of course, unique to each device. There is always no required capacity, but only those that are designed for running from outlet to outlet within the city.
You begin to scold manufacturers especially loudly when you find yourself in a force majeure situation. You are left without communication because your communicator died in the cold. You can’t capture a good moment because the original battery on the camera has run out, and a spare one from the company costs $50. Or you sit and get bored because the laptop only lasted for an hour.
But you can assemble a battery yourself, which will be limited by only two parameters: price per watt-hour and energy density. You will choose all other characteristics yourself.
The article was written for amateurs and by an amateur.
Only one “but”. This article is NOT about batteries larger than a few kilowatt-hours.
Theory on fingers
Element, cell, "jar", "battery"- something that accumulates and releases energy. All battery characteristics depend on the battery cells.
Battery- this is already a set of many elements. Several cells are connected into a battery when the characteristics of one cell are not enough. If you connect in series, the voltage increases. If in parallel, the battery capacity increases. It may include not only banks, but also all sorts of control electronics.
Voltage- this is the force with which the battery can shock the consumer. This is only a characteristic of the battery and does not depend on the consumer. 7 Measured in volts (V).
Current strength- the larger it is, the more electricity the consumer consumes. Measured in amperes (A).
Capacity- battery characteristics, measured in ampere-hours (Ah). For example, a capacity of 2Ah means that the battery can supply a current of 1A for two hours and 2A for one hour.
The battery capacity also depends on the discharge current. Typically, the larger it is, the smaller the capacity. Battery manufacturers usually indicate the capacity obtained when discharging with some meager current of 100mA.
The characteristics of a Li-ion battery are shown on the right, which is discharged at different current levels. The higher the current, the lower the discharge curve.
C- a letter of the Latin alphabet that measures the ratio of current to battery capacity, that is, how many times the current exceeds the capacity. If a battery has a capacity of 2Ah and is discharged at a current of 4A, then we can say that it is discharged at a current of 2C. The whole point is that the larger the battery capacity, the easier it is for it to supply current, and therefore this characteristic is more convenient to use than just amperes.
Energy- a characteristic that allows you to compare batteries with different voltages. Measured in watt-hours, it is roughly calculated by multiplying the battery voltage by its capacity. Numerically equal to the area of the figure under the discharge curve.
Parrots capacity and watt-hours of energy
Let's assume we have two batteries of the same capacity - 2200mAh. But one of them is lithium-ion, and the other is nickel-metal hydride.
Question: Does this mean that both batteries have the same amount of energy? Will the same device run on both cans for the same amount of time?
In fact, looking only at the capacity characteristic, one cannot compare energy, which the battery can accumulate and release. To do this, you need to know the rated voltage on it.
You can roughly estimate the amount of energy in watt-hours by multiplying the rated voltage of the battery by its capacity. And we will get:
- For NiMH: 1.2 volts * 2.2 amp hours = 2.64 watt hours
- For Li-ion: 3.7 volts * 2.2 ampere hours = 8.14 watt hours
That the energy of a Li-ion battery of the same capacity is 3 times more than NiMH.
But this is just a rough estimate. So, a voltage of 1.2 volts on a NiMH cell is the maximum voltage corresponding to a fully charged battery. When discharged, it will only drop, and the actual energy will be slightly less than 2.64 watt-hours. However, this is the method of calculating battery energy that we will use to compare their characteristics.
How to assemble a battery
How to assemble a battery Why assemble it yourself? Yes, because batteries are an area where the finished product is always crap. They are always unreasonably expensive. Always not
The Suzuki SV400S ’98 motorcycle I bought last fall almost immediately needed a new battery - the one that was instantly discharged did not always turn on the 35-watt xenon, and the starter turned somehow sluggishly and reluctantly. After another shameful start “from the pusher”, I went to the sites in search of a new battery. And almost immediately it started working - a new battery for my Susa from any decent manufacturer cost at least 3 thousand rubles. And this is for prehistoric lead batteries, low-capacity, heavy, with low current output! Many people know that most lead batteries have such an unpleasant “feature” - with a declared capacity of 12 Ah, only half the capacity can be safely used, i.e. about 6 Ah. Further discharge leads to accelerated battery degradation and prompt replacement. The exception is batteries from the “Deep Cycle” series - but how often have you seen such an inscription?)))
After digging around the Internet a little more, I found a more interesting option - batteries assembled from LiFePo4 cells.
Carefully! Lots of strange letters and pictures
Lithium-iron chemistry is quite safe, the elements are capacious and lighter than lead. Many manufacturers also talk about a 3-4 times increase in the life of such batteries, provided they are used correctly. And the capacity of the elements is honest, good elements can be discharged almost completely without damage to them and without a drop in current output as they are discharged! In addition, they are also more frost-resistant than lead. I found an option suitable in size and parameters - Shorai LFX12A1-BS12
So what do we have? The container is marked in “lead equivalent”, i.e. we read 12 Ah - we still have the same 6 Ah available! For that kind of money - I don't agree. A quick search of information from other manufacturers of similar batteries also did not please me - everywhere there is a small capacity, where it is honestly marked, and where it is again halved, “PB EQ”.
You say it's an ambush. Not for the DIYer))
Next there will be a lot of terminology that will be understandable to modellers, electricians and fellow DIYers. If anything, ask me in the comments or torment Google.
Two years ago, I became seriously interested in the possibility of assembling an electric bike from scratch, so I assembled it, and for the past year and a half I have been using it for its intended purpose. The traction battery was assembled from large quantity elements and electronics to monitor its condition. This is what it looks like without the cover:
The number of wires scares me too, yes)
The skills and information gained during the process were very helpful in assembling the new battery.
So, introductory: LiFePo4 elements, maximum capacity within the dimensions of a lead battery, maximum current output, control system for a long happy life, minimum price.
Having once again dug through the wilds of the network, I found several suitable options, and two of them became finalists:
A123 ANR26650M1A
rated voltage 3.3V
nominal capacity 2.3 Ah
rated discharge current 30C (69A per element)
maximum discharge current up to 60C (up to 138A per element)
rated charging current 10C (up to 23A per cell)
dimensions 26mm x 66.5mm
weight 70g.
rated voltage 6.6V (3.3V for each pair of elements)
nominal capacity 3.6 Ah (1.8 Ah per cell)
rated discharge current 30C (54A per element)
maximum discharge current up to 40C (up to 72A per element)
rated charging current 2C (up to 3.6A per cell)
dimensions 139mm x 21mm x 45mm
weight 262g.
The volume available to us fits 24 A123 cells (4S6P circuit, capacity 13.8 Ah, charging current up to 138A, discharge current 414A/828A, weight 1680g) or 8 Zippy batteries (4S8P circuit, capacity 14.4 Ah, charging current up to 28 ,8A, discharge current 432A/576A, weight 2100g).
Everything is great and joyful, but now such an important factor as cost begins to influence. 24 A123 cells will cost approximately 6000 rubles, 8 Zippy batteries will cost 5600 rubles, all with delivery. How much? That's what I thought too.
Therefore, I moderated my appetites somewhat and ordered 6 Zippy batteries, which cost me 4200 rubles. The parameters, of course, turned out to be more modest, but still pleasing to the eye - 4S6P circuit, capacity 10.8 Ah, charging current up to 21.6A, discharge current 324A/432A, weight 1570g.
And in addition, fortunately everything is in one store, I also took this little thing, which in the world is called Battery Checker & Balancer
This small gadget will take care of the health of the battery, in other words, it will equalize the voltage of the battery cells relative to each other. The only “but” is that the tester is designed primarily for LiPo batteries, not LiFePo4, so the battery charge in % will be displayed incorrectly. This does not interfere with balancing the elements. Therefore, I simply covered the left corner of the screen with the battery charge indicator - it’s confusing)
Well, some small things - balancing cables for the tester and protective caps. Handy! ©
Then, with the help of Russian Post, there was a short break - the first parcel took about 1.5 months, the second 2.5 months.
Finally everything arrived and I balanced all the batteries individually on the model charger. This is to avoid getting a small “badabum” when connecting batteries to each other. At the same time I checked the capacity, the stability of the voltage on the elements during discharge and in general...
The next stage is soldering and assembly:
1) Soldered in parallel 2 groups of 3 batteries each (2S6P + 2S6P)
from a different angle
Along the way, I fixed everything with reinforced tape - this is more reliable and less likely to damage the thin polyethylene shells of the elements.
2) This is what the battery filling looks like when assembled together
Two thick wires with connectors are needed to connect the battery parts in series with each other. Also visible are the 2S balancing pins from each part.
3) A plastic air duct cut into pieces will serve as a rigid battery case
5) I tied everything together with reinforced tape until I was completely satisfied, and made the contacts into “rings” from the terminals themselves (there were no suitable contact rings at hand)
6) Set it to be balanced, the run-up between the elements is minimal
In a couple of minutes everything comes down to a common denominator
And falls asleep so as not to waste my new battery
That's all, then the battery was installed in the proper place, and it works as it should.
Those. The xenon turns on quickly and without annoying blinking, the starter turns as if it had been wound up, and the headlights can be left on for an hour or two without draining the battery to zero. When I install the anti-theft system, I can also leave it on for much longer. I also love good light, so soon I will replace the 35W xenon lights with something better - 55/75W or even diodes. The battery allows)
In the next article I will tell you how I made a marker/brake signal from powerful diodes to replace halogen light bulbs.
DIY lithium ion battery
I decided that I would dedicate my first post to something more interesting than how I got to this life)) Motik. How and why I did it lithium battery
Element, cell, "jar", "battery"- something that accumulates and releases energy. All battery characteristics depend on the battery cells.
Battery- this is already a set of many elements. Several cells are connected into a battery when the characteristics of one cell are not enough. If you connect, the voltage increases. If - the battery capacity increases. It may include not only banks, but also all sorts of control electronics.
Voltage- this is the force with which the battery can shock the consumer. This is only a characteristic of the battery and does not depend on the consumer. Measured in volts (V).
Current strength- the larger it is, the more electricity the consumer consumes. Measured in amperes (A).
Capacity- battery characteristics, measured in ampere-hours (Ah). For example, a capacity of 2Ah means that the battery can supply a current of 1A for two hours and 2A for one hour.
The battery capacity also depends on the discharge current. Typically, the larger it is, the smaller the capacity. Battery manufacturers usually indicate the capacity obtained when discharging with some meager current of 100mA.
The characteristics of a Li-ion battery are shown on the right, which is discharged at different current levels. The higher the current, the lower the discharge curve.
C- a letter of the Latin alphabet that measures the ratio of current to battery capacity, that is, how many times the current exceeds the capacity. If a battery has a capacity of 2Ah and is discharged at a current of 4A, then we can say that it is discharged at a current of 2C. The whole point is that the larger the battery capacity, the easier it is for it to supply current, and therefore this characteristic is more convenient to use than just amperes.
Energy- a characteristic that allows you to compare batteries with different voltages. Measured in watt-hours, it is roughly calculated by multiplying the battery voltage by its capacity. Numerically equal to the area of the figure under the discharge curve.
Parrots capacity and watt-hours of energy
Let's assume we have two batteries of the same capacity - 2200mAh. But one of them is lithium-ion, and the other is nickel-metal hydride.
Question: Does this mean that both batteries have the same amount of energy? Will the same device run on both cans for the same amount of time?
vs 
In fact, looking only at the capacity characteristic, one cannot compare energy, which the battery can accumulate and release. To do this, you need to know the rated voltage on it.
You can roughly estimate the amount of energy in watt-hours by multiplying the rated voltage of the battery by its capacity. And we will get:
- For NiMH: 1.2 volts * 2.2 amp hours = 2.64 watt hours
- For Li-ion: 3.7 volts * 2.2 ampere hours = 8.14 watt hours
That the energy of a Li-ion battery of the same capacity is 3 times more than NiMH.
But this is just a rough estimate. So, a voltage of 1.2 volts on a NiMH cell is the maximum voltage corresponding to a fully charged battery. When discharged, it will only drop, and the actual energy will be slightly less than 2.64 watt-hours. However, this is the method of calculating battery energy that we will use to compare their characteristics.
Battery types
| type | NiMH | Li-ion | Li-polymer | LiFePO 4 | Lead Acid |
| rated voltage per cell | 1.2V | 3.7V | 3.3V | 2.105V | |
| voltage range | 0-1.2V | 2.5-4.2V | 2.0-3.65V | 1.75-2.1V | |
| number of charge/discharge cycles until 20% capacity is lost | 500-1500 | 1000 | 2000-8000 | 200-800 | |
| shelf life up to loss of 20% capacity | up to 2 years | ~1.5 years | 5-10 years | ||
| simple charge time | until 16 o'clock | 1-2 hours | 45 minutes | 6-10 hours | |
| fast charge time | 1-2 hours | 45 minutes | 15 minutes | 15 minutes | 1-2 hours |
| energy density, watt-hours per kg | 80 | 200 | 150 | 100 | 40 |
| price per watt hour | $0.5-$1.3 | $0.5-$0.7 | from $0.3 | $0.5-$2.2 | $0.1-$0.3 |
NiMH - nickel metal hydride
Batteries of this type are obsolete and added for comparison. But sometimes it makes sense to think about buying them - for example, when you need to make a replacement for a dead NiCd or NiMH battery. These are the ones they put in cheap radio-controlled models.
−
They are capricious in charging and require complex devices to quickly charge.
−
They lose charge over time. LSD (Long Self Discharge) batteries do not have this drawback.
−
They have a “memory effect”, that is, they temporarily lose part of their capacity during partial discharges. They only love full ranks. LSD batteries also do not have this drawback.
−
They have low energy density.
+
Under- and overcharging is harmful to them, but not dangerous, so these cans can be used to form a battery just like that, without protective electronics.
The most popular size for these “cans” is regular AA, that is, the size of a AA battery.
Li-ion - lithium-ion
+ They have the highest energy density.
− Fast discharged when used in cold weather.
You may have experienced this harmful property if you have used mobile phone outside in winter. The battery magically dies and you are left without communication.
−
They deteriorate when discharged below 2.5V.
−
Explosive when overcharged above 4.2V.
A popular standard size for lithium-ion “cans” is 18650 (18mm wide and 65mm long). These are the ones used in laptop batteries. You may never see them behind the plastic battery case, but sometimes you can feel them there. The same ones are used in the Tesla Roadster electric sports car.
Li-polymer - lithium polymer
+
Fully compatible with Li-ion.
+
Unlike Li-ion, they can deliver strong currents - 10-40C.
+
Can be of any thickness and shape. Suitable for powering very miniature devices, like spy gadgets.
+
They are usually sold with an already assembled battery, with protective boards and cables for balancing - convenient!
−
Even more explosive and fire hazardous.
−
They work even worse in the cold. Look, for example, at this discharge graph:
LiFePO 4 - lithium iron phosphate
Further evolution of lithium batteries. Batteries of the future. Unlike Li-ion, they:
+
are not afraid of frost;
+
not fire hazardous;
+
deliver currents up to 50C;
+
can be charged with high current in 15 minutes;
+
have a huge number of charge-discharge cycles (2000-8000 before losing 20% capacity);
+
practically not subject to loss of capacity during storage.
Disadvantages compared to Li-ion:
−
are more expensive and have less capacity;
−
have lower energy intensity;
−
not compatible with conventional Li-ion cells due to a different voltage range - 2-3.65V.
− And just like Li-ion, they require compliance with their voltage range - 2-3.65V.
The most respected company in the LiFePO 4 battery market is A123 Systems. She also developed this technology.
The popular standard size for “cans” - 26650 (26 mm wide and 65 mm long) - was introduced by the same A123 Systems.
LiFeYPO 4 - lithium iron yttrium phosphate
A type of lithium battery that I know nothing about, except that adding yttrium increases the number of charge-discharge cycles. Well, we'll wait and see.
Lead-Acid - lead-acid
−
They have the lowest energy density.
−
Charges slowly - up to several hours!
−
At high currents (by their standards, this is what is above 0.1C) they may not give up even half of the battery capacity.
−
Very sensitive to temperatures.
−
They have a small number of charge-discharge cycles - from 200 with harsh handling to 800 with gentle handling.
−
In the case of a serviceable battery, it requires care.
+
Damn cheap!
I would like to mention the good old lead-acid batteries here. Because every reader will probably have a question - why the hell is all this needed when you can buy a 12-volt box at any auto parts store? Why won't we consider them here?
- Firstly, because lead-acid batteries are sold already assembled into a 6-12V battery, which does not fit with the title of this article.
- Secondly, lead-acid batteries are such a broad topic that they deserve a couple more articles.
- Thirdly, I find them too heavy for all sorts of interesting things.
Comparison
There are many tables on the Internet comparing characteristics different types batteries. And all such tables have the same drawback - they compare spherical horses in a vacuum. So I made my own, with specific examples:
| type | example | watt hours per: | $ per watt-hour of capacity | cents per watt-hour of energy | |
|---|---|---|---|---|---|
| kg | liter | ||||
| NiMH | Turnigy AA LSD 2550mAh from hobbyking, price without delivery | 99 | 370 | 0.77 | 0.148 (500 cycles) |
| Eneloop AA LSD 2000mAh from eBay | 89 | 309 | 1.24 | 0.076 (1500 cycles) | |
| Li-ion | 132 | 425 | 0.67 | 0.067 (1000 cycles) | |
| 145 | 391 | 0.51 | 0.051 (1000 cycles) | ||
| 360 | 675 | 0.79 | 0.079 (1000 cycles) | ||
| 251 | 479 | 0.84 | 0.084 (1000 cycles) | ||
| LiPo | Hobbying battery 14.8V 5Ah, price excluding delivery | 140 | 269 | 0.30 | 0.030 (1000 cycles) |
| LiFePO 4 | 111 | 269 | 1.11 | 0.045 (2000 cycles) | |
| A123 18650 from Hobbyking, price without delivery | 66 | 219 | 2.22 | 0.111 (2000 cycles) 0.027 (8000 cycles) |
|
| A123 ANR26650M1A from ebay | 104 | 220 | 1.30 | 0.065 (2000 cycles) 0.016 (8000 cycles) |
|
| “can” for 8Ah from ev-power.eu, with 20% VAT | 98 | 209 | 0.65 | 0.032 (2000 cycles) | |
| large “can” for 20Ah, from the same place, with 20% VAT | 70 | 141 | 0.52 | 0.026 (2000 cycles) | |
| Chinese “battery” for 36 megawatt hours | - | - | 0.07 | ? | |
| LiFeYPO 4 | Winston (Thunder Sky) for 100Ah from ebay | 91 | ? | 0.42 | 0.014 (3000 cycles) |
| Lead Acid | random maintenance free battery 12V/17Ah | 40 | 88 | 0.23 | 0.046 (500 cycles) |
| random car battery 12V/50Ah | 46 | 91 | 0.13 | 0.026 (500 cycles) | |
For example, I made the following conclusions:
- LiFePO 4 is the future. In the long run, they beat even lead-acid batteries in price. Well, even more so with the advantages of iron phosphate and the disadvantages of lead. This is the only thing from which electric vehicles can be assembled. And the only thing that can be dragged out into the cold.
- The highest energy density is y. If you have to carry them on yourself, then this is the most reasonable choice.
- Sometimes it makes sense to take a ready-made lithium-polymer battery and not worry about it.
Connecting elements into a battery
Serial connection
This is when the positive (+) pole of each element is connected to the negative (−) pole of the next:
In this case, the voltages of the elements add up, but the capacitance remains the same.
Series connected elements require balancing.
The fact is that even cans from the same batch have slightly different characteristics. And they charge at different speeds.
Let's take a battery of three series-connected elements. The voltage on a fully charged element is 4.2V. This means that a fully charged battery should have a voltage of 12.6 volts. Some of the elements - for example, in the middle - may charge faster, and at a voltage of 12.2V we will have the following picture:
If you continue charging, the battery in the middle will be recharged to a voltage of 12.6V:
The result is combustion of the element and painful death from suffocation. To prevent this from happening, balancers are used that take on part of the current if the voltage on a separate element approaches critical:
And as a result, all elements will be fully charged:
Parallel connection
This is when the positive (+) poles are connected to the positive ones, and the negative (−) poles are connected to the negative ones:
When the elements are connected in parallel, their voltage remains the same, but the capacitances add up. It turns out to be one big battery.
Balancing is not required in the case of a pure parallel connection. However, if the battery also has serial connections - as in this 4S2P circuit - then it would be a good idea to solder a balancing cable:
About soldering lithium cells
Lithium batteries cannot be soldered. Heating with a soldering iron will damage them.
On the other hand, for precise solder balancing recommended, since excess resistance can distort the voltage data received by the charger.
So if you really want to, then you can. But in this case, it’s better to take “cans” with terminals and touch them with a soldering iron for no longer than a couple of seconds.
If you still find the courage to solder cans into a battery, then read the unofficial manual in English from Hyperion HK Ltd. for soldering batteries from A123. This process is described there in detail, with illustrations.
If not, then let's look at alternative options.
 | Can be used as contacts. They are very strong - you can’t separate them from each other. The outside is coated with nickel or zinc, which do not oxidize. The contact with the jar is excellent. For complete happiness, you can solder wires to them, but do this very carefully: the Curie temperature for them - at which the magnets turn into a pumpkin - is about 300 degrees. You can only use low-melting solder and a heat-stabilized soldering iron - something like this. |
 | Or buy a special holder, like for regular AA/AAA batteries. The big advantage of this solution is that the batteries will not be tightly soldered, and spare charged ones can be inserted in place of dead cans. And you don’t need to buy expensive chargers with balancers - you can charge 2 batteries at a time. |
| On eBay you can find such a ready-made miracle battery holder with built-in protection for Li-ion elements. And you don’t need to solder anything - just insert unprotected Li-ion batteries and go. |
Protection of cans from overdischarge and overcharge
As I already said, lithium cells will forgive you for neither one nor the other.
The easiest way to avoid this problem is to use protected (protected) batteries. These are the ones they buy for everyone LED lights. Protected batteries have this small scarf inside the case:
Another option is to put one large board for the entire battery. For example, this one. Here is its connection diagram in the 4S2P configuration - 4 batteries connected in series, 2 parallel batteries each:
Where P+ and P- are terminals to the charger or consumer.
Don't forget that LiFePO 4 is not compatible with regular Li-ion cells, and they require special protective boards.
Pulse width modulators, or DC-DC converters
These are devices that will do what you need from the voltage that the battery gives you. Because often, depending on the voltage that the battery produces, the device will either burn out or not work, or the former with a fully charged battery and the latter with a discharged one.
You can solder such a simple device yourself. Here are instructions for beginners from DI HALT. If you are lazy, then welcome to ebay.
Like any device, DC-DC converters have their own permissible voltage and current range. Calculate in advance how much your consumer will need. In case of too high currents, the converter needs to be cooled, or even replaced with a more powerful option.
Laptop battery repair
There's no point in buying new battery for a laptop, when you can buy lithium-ion “cans” for two or three times cheaper and replace the old ones with them. Here is the repair process in the famous video:
http://www.youtube.com/watch?v=BtqRvAu71Gw
It remains only to highlight a few things.
- Li-ion batteries are afraid of high temperatures, and especially of a soldering iron. It is recommended to select only “cans” with terminals for soldering and not hold the soldering iron for more than a couple of seconds. If you are not careful, you can ruin the battery!
- Li-ion batteries are explosive and fire hazardous if overcharged. Double check that your cans are connected correctly.
- Some laptop manufacturers put clever electronics into their batteries that are essentially protection against repairs. First, read on the Internet about the experience of repairing batteries for laptops from your series. It's possible that nothing will work out. All claims in this case are to the manufacturer.
Autonomous charging of mobile phones and everything else
This thing will come in handy on trips, hikes - anywhere there are problems with sockets. For this you will need:
 | $14.07 | $2.70 | |||
 | battery holder | $1.45 |  | piece of USB extension cable | ? |
 | $3.08 | ||||
You will also need a multimeter (tester) that can withstand current up to 10A.
- First you need to solder the wires from the battery holder to the PWM: black to IN-, red to IN+.
- Then you will need to configure the PWM. If you don't do this, this device can burn your phone!
- Switch the multimeter to DC voltage measurement mode and touch the OUT+ and OUT- contacts with the probes. The multimeter will show open circuit voltage. Take a small screwdriver and twist the first potentiometer (the one on the left in the photo) until the multimeter shows a voltage of 5 volts.
- Then switch the multimeter to DC current mode. Also touch the probes to OUT+ and OUT-. Adjust the strength current short circuit potentiometer on the right to 1 ampere.
- The potentiometer in the middle usually does not need to be touched.
- Remove the batteries from the holder.
- Connect the USB socket to the PWM. To do this, cut it off from the USB extension cable and spread the cut end. You need to solder the black wire to the OUT- pin, the red wire to the OUT+ pin, but you don’t need to touch the green, white and screen. You can cut them to hell if they get in the way. As long as they don't end up with anything.
All. Now you can insert the batteries into the holder, the broom with plugs into the USB socket and charge anything, anywhere. The big advantage of this scheme is that the batteries are not tightly screwed in, and they can be replaced with spare ones when they die.
You can charge your mobile phone with such nonsense five times. If you just need long-term operation of your mobile phone, you can remove the battery from it - in this case, energy will be spent more efficiently.
Battery for Raspberry Pi
I checked the recipe. Does not work! Stay tuned for further edits.
The charging process in the “normal” (classic) mode looks something like this: the first 4-6 hours are the main battery charging cycles, and then “adaptive topping up” of the battery capacity occurs at different frequencies and intervals, for about another 2-4 hours. When charging “overnight”, as a rule, by the morning the battery is fully charged to its nominal capacity.
In the “adaptive” (AUTO) mode, the charger can charge the battery to 100% capacity in 50 minutes to 2 hours. (highly depends on the capabilities of the battery itself, and the charge currents that the battery can accept. For fast charging Battery currents can reach 0.8-1.5C)
7 Yes, I know that if you short-circuit the battery, the voltage at the terminals will drop to zero.
Nowadays lithium batteries are gaining more and more popularity. Especially finger ones, like 18650 , at 3.7 V 3000 mA. I have no doubt that in another 3-5 years they will completely replace nickel-cadmium. True, the question about their charging remains open. If everything is clear with old batteries - collect them in a battery and through a resistor to any suitable power supply, then this trick does not work here. But how then can you charge several pieces at once without using expensive branded balancing chargers?
Theory
For series connection of batteries, usually to positive electrical diagram connect the positive terminal of the first battery in series connection. The positive terminal of the second battery is connected to its negative terminal, etc. The negative terminal of the last battery is connected to the negative terminal of the unit. The resulting battery in series connection has the same capacity as a single battery, and the voltage of such a battery is equal to the sum of the voltages of the batteries included in it. This means that if the batteries have the same voltage, then the battery voltage is equal to the voltage of one battery multiplied by the number of batteries in the battery.
The energy accumulated in the battery is equal to the sum of the energies of the individual batteries (the product of the energies of the individual batteries, if the batteries are the same), regardless of whether the batteries are connected in parallel or in series.
Lithium-ion batteries cannot simply be connected to a power supply unit - the charging currents on each element (bank) must be equalized. Balancing is carried out when charging the battery, when there is a lot of energy and it can not be saved much, and therefore, without any significant losses, you can use the passive dissipation of “excess” electricity.
Nickel-cadmium batteries do not require additional systems, since each link, when its maximum charge voltage is reached, stops receiving energy. Signs of a fully charged Ni-Cd are an increase in voltage to certain value, and then it drops by several tens of millivolts, and the temperature rises - so that the excess energy immediately turns into heat.
The opposite is true for lithium batteries. Discharge to low voltages causes degradation of chemistry and irreversible damage to the element, with increasing internal resistance. In general, they are not protected from overcharging, and you can waste a lot of extra energy, thereby dramatically reducing their service life.
If we connect several lithium cells in a row and feed them through clamps at both ends of the block, then we cannot control the charge of individual cells. It is enough that one of them will have a slightly higher resistance or a slightly lower capacitance, and this link will reach a charge voltage of 4.2 V much faster, while the rest will still have 4.1 V. And when the voltage of the entire package reaches charge voltage, it may be that these weak links are charged to 4.3 Volts or even more. With each such cycle, the parameters will deteriorate. In addition, Li-Ion is unstable and, if overloaded, can reach high temperatures and, consequently, explode.
Most often, a device called a “balancer” is installed at the output of the charging voltage source. Simplest type The balancer is a voltage limiter. It is a comparator that compares the voltage on a Li-Ion bank with a threshold value of 4.20 V. Upon reaching this value, a powerful transistor switch is opened, connected in parallel to the element, passing most of the charge current through itself and converting the energy into heat. In this case, the can itself receives an extremely small part of the current, which practically stops its charge, allowing its neighbors to recharge. The voltage equalization on the battery cells with such a balancer occurs only at the end of the charge when the elements reach a threshold value.
Simplified diagram of a balancer for a battery
Here is a simplified circuit diagram of a current balancer based on the TL431. Resistors R1 and R2 set the voltage to 4.20 Volts, or you can choose others depending on the type of battery. The reference voltage for the regulator is removed from the transistor, and already at the border of 4.20 V, the system will begin to open the transistor slightly to prevent exceeding the specified voltage. A minimal increase in voltage will cause very fast growth transistor current. During tests, already at 4.22 V (an increase of 20 mV), the current was more than 1 A.
Basically anyone fits here. PNP transistor, operating in the range of voltages and currents that interest us. If the batteries are to be charged with a current of 500 mA. The calculation of its power is simple: 4.20 V x 0.5 A = 2.1 V, and this is how much the transistor must lose, which will probably require some cooling. For a charging current of 1 A or more, the power loss increases accordingly, and it will become increasingly difficult to get rid of the heat. During the test, several different transistors were tested, in particular BD244C, 2N6491 and A1535A - they all behave the same.
The voltage divider R1 and R2 should be selected so as to obtain required voltage restrictions. For convenience, here are a few values, after applying which we will get the following results:
- R1 + R2 = Vo
- 22K + 33K = 4.166 V
- 15K + 22K = 4.204 V
- 47K + 68K = 4.227 V
- 27K + 39K = 4.230 V
- 39K + 56K = 4.241 V
- 33K + 47K = 4.255 V
This is an analogue of a powerful zener diode loaded with a low-resistance load, the role of which here is played by diodes D2...D5. Microcircuit D1 measures the voltage at the plus and minus of the battery and if it rises above the threshold, it opens a powerful transistor, passing all the current from the charger through itself. How all this is connected together and to the power supply - see below.
The blocks turn out to be really small, and you can safely install them directly on the element. You just need to keep in mind that the potential of the negative pole of the battery arises on the transistor body, and you must be careful when installing common radiator systems - you must use insulation of the transistor bodies from each other.
Tests
Immediately 6 pieces of balancing blocks were needed to simultaneously charge 6 18650 batteries. The elements are visible in the photo below.
All elements were charged exactly to 4.20 volts (the voltage was set by potentiometers), and the transistors became hot, although there was no additional cooling - charging with a current of 500 mA. Thus, we can safely recommend this method for simultaneous charging of several lithium batteries from a common voltage source.
Discuss the article SIMULTANEOUS CHARGING OF SEVERAL BATTERIES
The industry has been making screwdrivers for a long time, and many people have older models with nickel-cadmium and nickel-metal hydride batteries. Converting a screwdriver to lithium will improve the performance characteristics of the device without buying a new tool. Now many companies offer services for converting screwdriver batteries, but you can do it yourself.
Benefits of lithium-ion batteries
Nickel-cadmium batteries have a low price, withstand many charging cycles, and are not afraid of low temperatures. But the battery capacity will decrease if you charge it before it is completely discharged (memory effect).
Lithium-ion batteries have the following advantages:
- high capacity, which will ensure longer operating time of the screwdriver;
- smaller size and weight;
- Retains charge well when not in use.
But a lithium battery for a screwdriver does not withstand full discharge well, so factory tools on such batteries are equipped with additional circuit boards that protect the battery from overheating, short circuit, and overcharging to avoid explosion or complete discharge. When the microcircuit is installed directly into the battery, the circuit opens if the unused battery is located separately from the tool.
Difficulties in reworking
IN Li-Ion batteries There are objective disadvantages, such as poor performance at low temperatures. In addition, when converting a screwdriver to 18650 lithium batteries, you may encounter a number of difficulties:
- The 18650 standard means that the diameter of one battery cell is 18 mm with a length of 65 mm. These dimensions do not coincide with the dimensions of the nickel-cadmium or nickel-metal hydride elements previously installed in the screwdriver. Replacing batteries will require placing them in a standard battery case, plus installing a protective microcircuit and connecting wires;
- The output voltage for lithium cells is 3.6 V, and for nickel-cadmium cells - 1.2 V. Let's say the nominal voltage old battery– 12 V. Such a voltage cannot be provided when connecting Li-Ion elements in series. The scope of voltage fluctuations during charge-discharge cycles of an ion battery also changes. Accordingly, converted batteries may not be compatible with the screwdriver;
- Ion batteries differ in the specifics of their operation. They do not withstand overcharge voltages greater than 4.2 V and discharge voltages less than 2.7 V until they fail. Therefore, when the battery is rebuilt, a protective board must be installed in the screwdriver;
- The existing charger may not be able to be used for a screwdriver with a Li-Ion battery. You will also need to remake it or purchase another one.
Important! If a drill or screwdriver is cheap and not of very high quality, then it is better not to remodel it. This may cost more than the cost of the tool itself.
Battery selection
Screwdrivers often use 12 V batteries. Factors to consider when choosing a Li-Ion battery for a screwdriver:
- Such instruments use elements with high discharge current values;
- In many cases, the capacity of the element is inversely related to the discharge current, so you cannot select it based on capacity alone. The main indicator is current. The value of the operating current of the screwdriver can be found in the tool passport. Usually it is from 15 to 30-40 A;
- When replacing a screwdriver battery with a Li-Ion 18650, it is not recommended to use cells with different capacity values;
- Sometimes there are tips to use a lithium battery from an old laptop. This is absolutely unacceptable. They are designed for a much lower discharge current and have unsuitable technical characteristics;
- The number of elements is calculated based on the approximate ratio - 1 Li-Ion to 3 Ni-Cd. For a 12-volt battery, you will need to replace 10 old cans with 3 new ones. The voltage level will be slightly reduced, but if you install 4 elements, then increased voltage will shorten the life of the electric motor.
Important! Before assembly, it is necessary to fully charge all elements for equalization.
Disassembling the battery case
The case is often assembled using self-tapping screws, other options are assembled using latches or glue. The glued block is the most difficult to disassemble; you have to use a special hammer with a plastic head so as not to damage parts of the body. Everything from inside is removed. You can reuse only the contact plates or the entire terminal assembly for connecting to a tool or charger.
Battery Cell Connection
CompoundLi– Ionbatteries for screwdriverperformed in several ways:
- The use of special cassettes. The method is fast, but the contacts have a high transition resistance and can quickly be destroyed by relatively high currents;
- Soldering. A method suitable for those who know how to solder, since you need to have certain skills. Soldering must be done quickly, because the solder cools quickly, and prolonged heating can damage the battery;
- Spot welding. Is the preferred method. Not everyone has a welding machine; such services can be provided by specialists.
Important! The elements must be connected in series, then the battery voltage is added, but the capacity does not change.
At the second stage, the wires are soldered to the contacts of the assembled battery and to the protective board according to the connection diagram. Wires with a cross-sectional area of 1.5 mm² are soldered to the contacts of the battery itself for power circuits. For other circuits, you can take thinner wires - 0.75 mm²;
A piece of heat shrink tubing is then placed over the battery, but this is not necessary. You can also put heat shrink on the protective microcircuit to isolate it from contact with the batteries, otherwise sharp solder protrusions can damage the shell of the element and cause a short circuit.
Further battery replacement consists of the following steps:
- The disassembled parts of the body are well cleaned;
- Since the dimensions of the new battery cells will be smaller, they need to be securely fixed: glued to the inner wall of the case with Moment glue or sealant;
- The positive and negative wires are soldered to the old terminal block, it is placed in its original place in the housing and fixed. The protective board is laid, the parts of the battery pack are connected. If they were previously glued, then “Moment” is used again.
The lithium-ion battery of the screwdriver will not be able to function properly without the BMS protection board. The copies sold have different parameters. The BMS 3S marking assumes, for example, that the board is designed for 3 elements.
What you need to pay attention to in order to choose a suitable microcircuit:
- The presence of balancing to ensure uniform charge of the elements. If it is present, the description of the technical data should include the value of the balancing current;
- The maximum value of operating current that can be withstood for a long time. On average, you need to focus on 20-30 A. But this depends on the power of the screwdriver. Low-power ones need 20 A, high-power ones – from 30 A;
- Voltage at which the batteries are switched off when overcharging (about 4.3 V);
- The voltage at which the screwdriver turns off. This value must be selected based on the technical parameters of the battery cell (minimum voltage - about 2.6 V);
- Overload protection current;
- Resistance of transistor elements (select the minimum value).
Important! The magnitude of the operating current during overload does not have of great importance. This value is adjusted to the operating load current. In case of short-term overloads, even if the tool has turned off, you must release the start button, and then you can continue to work.
Whether the controller has an autostart function can be determined by the presence of the “Automatic recovery” entry in the technical data. If there is no such function, then in order to start the screwdriver again after the protection has tripped, you will need to remove the battery and connect it to the charger.
Charger
The lithium-ion battery of the screwdriver cannot be charged by connecting it to a conventional power supply. A charger is used for this. The power supply simply produces a stable charge voltage within specified limits. And in the charger, the determining parameter is the charge current, which affects the voltage level. Its meaning is limited. The charger circuit contains nodes responsible for stopping the charging process and other protective functions, for example, shutdown in case of incorrect polarity.
The simplest charger is a power supply with a resistance included in the circuit to reduce the charging current. Sometimes they also connect a timer that fires after a set time period has passed. All of these options are not conducive to long battery life.
Charging methodsLI Ionbatteries for screwdriver:
- Using a factory charger. Often it is also suitable for charging a new battery;
- Reworking the charger circuit, with the installation of additional circuit elements;
- Purchase of a ready-made memory. A good option– IMax.
Let's say there is an old Makita DC9710 charger for charging a 12 V Ni-Cd battery, which has an indication in the form of a green LED signaling the end of the process. The presence of a BMS board will allow you to stop the charge when the specified voltage limits per element are reached. The green LED will not light up, but the red one will simply go out. The charge is complete.
The Makita DC1414 T charger is designed to charge a wide range of batteries 7.2-14.4 V. In it, when the protective shutdown is triggered at the end of the charge, the indication will not work correctly. The red and green lights flash, which also signals the end of the charge.
The cost of replacing screwdriver batteries with lithium-ion ones depends on the power of the tool, the need to buy a charger, etc. But if the drill/driver is in good functional condition and the charger does not require major alteration or replacement, then for a couple of thousand rubles you can get an improved power tool with increased battery life.
Video